EX-5.1

Exhibit 5.1


	200 Clarendon Street Boston, Massachusetts 02116 Tel: +1.617.948.6000 Fax: +1.617.948.6001 www.lw.com

	FIRM / AFFILIATE OFFICES
October 1, 2024 Seres Therapeutics, Inc. 101 Cambridgepark Drive Cambridge, MA 02140	Austin Beijing Boston Brussels Century City Chicago Dubai Düsseldorf Frankfurt Hamburg Hong Kong Houston London Los Angeles Madrid	Milan Munich New York Orange County Paris Riyadh San Diego San Francisco Seoul Silicon Valley Singapore Tel Aviv Tokyo Washington, D.C.

Re: Registration Statement on Form S-3; 14,285,715 shares of Common Stock, $0.001 par value per share

To the addressee set forth above:

We have acted as special counsel to Seres Therapeutics, Inc., a Delaware corporation (the “Company”), in connection with the resale from time to time by the selling stockholder named in the Registration Statement (as defined below) of up to 14,285,715 shares (the “Shares”) of the Company’s Common Stock, par value $0.001 per share. The Shares are included in a registration statement on Form S-3 under the Securities Act of 1933, as amended (the “Act”), filed with the Securities and Exchange Commission (the “Commission”) on the date hereof (the “Registration Statement”). This opinion is being furnished in connection with the requirements of Item 601(b)(5) of Regulation S-K under the Act, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement or the prospectus contained therein, other than as expressly stated herein with respect to the issue of the Shares.

As such counsel, we have examined such matters of fact and questions of law as we have considered appropriate for purposes of this letter. With your consent, we have relied upon certificates and other assurances of officers of the Company and others as to factual matters without having independently verified such factual matters. We are opining herein as to the General Corporation Law of the State of Delaware, and we express no opinion with respect any other laws.

Subject to the foregoing and the other matters set forth herein, it is our opinion that, as of the date hereof, the Shares have been duly authorized by all necessary corporate action of the Company, and are validly issued, and the Shares are fully paid and non-assessable.